The present invention relates to a disc player for reading information from an optical disc having ID regions, segmented into two regions in the direction of the track, in which record position information are preformatted and recorded.
A spindle control system as shown in FIG. 14 is known as the technique for driving an optical disc to rotate in a CAV (constant angular velocity) mode in an optically readable, disc player. Information is read out of a disc 1 being rotated by a spindle motor 2, by a pick-up (not shown). The spindle motor 2 includes means to generate a pulse signal (FG pulse signal) of which the frequency corresponds to a rotation speed of the motor. The FG pulse signal generated is applied to an error generating circuit 3. A reference clock signal of a predetermined frequency corresponding to a target angular speed of the motor is supplied to the error generating circuit 3. The error generating circuit 3 detects frequency and phase errors through the comparison of the clock signal and the FGpulse signal, and applies error signals dependent on the detection errors to a pulse width modulator (PWM) 4. The output signal of the PWM 4 passes through a low-pass filter (LPF) 5 and reaches a drive circuit 6.
Thus, the error signal is PWM processed and only its low frequency component is filtered out. The drive circuit 6 applies a drive signal, which is based on the error signal of the low frequency component, to the spindle motor 2. The spindle motor 2 is controlled so as to reduce the error detected by the error generating circuit 3 to zero (0), viz., so as to maintain the target angular velocity of the motor.
To read the disc 1 in a CLV (constant linear velocity) mode, it is required that the disc 1 is driven to rotate in accordance with a read signal (or a read position) To realize such a drive of the motor, a synchronizing (sync) signal is extracted from the read signal, and the angular velocity of the spindle motor 2 is controlled so that the sync signal has a predetermined frequency.
In connection with the sync-signal basis motor control, the Examined Japanese Patent Application Publication No. Hei 4-71269 discloses the following technique. In a situation where no sync signal is produced, e.g., when the disc player is started or when the pick-up is moved at high speed, the maximum value of the time interval (maximum reversal interval) from the leading edge of a data signal of the read signal to the next trailing edge is detected, and the angular velocity of the spindle motor is controlled so that the maximum reversal interval reaches a predetermined value.
At present, a high density recording disc, called a DVD (digital versatile disc), is increasing its market share. Some type of the DVD has a plural number of formats for recording information therein. A typical example of those DVDs is a DVD-RAM (DVD-random access memory) allowing information to be rewritten into the DVD itself.
The DVD-RAM, or a RAM type DVD, has the following disadvantage when no information is recorded therein or a small amount of information is recorded in a part thereof. In the RAM type DVD, data signals to be used for the control of the spindle motor are absent or, if present, are insufficient for the control. Therefore, the disc player frequently fails to detect the maximum reversal interval or the maximum/minimum time period.
ID regions are preformatted at predetermined angular spatial intervals in the surface of the DVD-RAM. Address information on the disc and information indicative of a groove track or a land track are stored in the ID regions. (The ID region will be described in detail later.) It is required that the disc player accurately detects the ID regions.